Vitamin D is often referred to as the ‘sunshine vitamin’, yet despite its availability through sunlight, vitamin D deficiency is one of the most common nutrient concerns worldwide. Unlike other vitamins, vitamin D functions more like a hormone, and every single cell in your body has a receptor for it.
Your body produces vitamin D from cholesterol when your skin is exposed to sunlight. It is also found in certain foods, such as fatty fish and fortified dairy products, though it is very difficult to get enough from diet alone. Because of the modern indoor lifestyle and the use of sun protection, deficiency is rampant, particularly in the UK where sunlight can be scarce during autumn and winter months.
Low levels of this crucial nutrient can lead to significant health issues, yet the symptoms are often subtle. Many people do not realise they are deficient until they undergo blood testing. Understanding the signs is the first step toward better health.
Here are the 10 essential signs of vitamin D deficiency to look for, backed by science.
1. Frequent Illness or Infections
One of the most critical roles vitamin D plays is keeping your immune system strong so you are able to fight off viruses and bacteria that cause illness. It directly interacts with the cells that are responsible for fighting infection.
If you find yourself becoming sick often, particularly with colds or the flu, low vitamin D levels may be a contributing factor. Several large observational studies have shown a link between a deficiency and respiratory tract infections like colds, bronchitis, and pneumonia.
A number of studies suggest that taking vitamin D supplements at a dosage of up to 4,000 IU daily may reduce the risk of respiratory tract infections. In the context of the UK climate, where sunlight is insufficient for synthesis from October to March, this connection is vital to monitor.
2. Fatigue and Tiredness
Feeling tired can have many causes, and vitamin D deficiency is often an overlooked one. Case studies have shown that very low blood levels can cause fatigue that has a severe negative effect on quality of life.
In one case, a woman who complained of chronic daytime headaches and fatigue was found to have a blood level of only 5.9 ng/mL. This is extremely low, as anything under 20 ng/mL is considered deficient. When she took a vitamin D supplement, her level increased to 39 ng/mL and her symptoms resolved.
Even blood levels that are not extremely low but borderline low may have a negative impact on your energy levels. It is not merely about sleep; it is about the cellular energy required for daily functioning.
3. Bone and Back Pain
Vitamin D is involved in maintaining bone health through a number of mechanisms. For one, it improves your body’s absorption of calcium. Bone pain and lower back pain may be signs of inadequate vitamin D levels in the blood.
Large observational studies have found a relationship between a deficiency and chronic lower back pain. Researchers have noted that those with a deficiency were more likely to have back pain, including severe back pain that limited their daily activities.
If you experience deep, aching pain in your bones—often distinguishable from muscle soreness—it is worth consulting a GP. This is distinct from sharp injury pain; it is often a dull, pervasive ache.
4. Depression or Low Mood
A depressed mood may also be a sign of nutritional deficiency. In review studies, researchers have linked vitamin D deficiency to depression, particularly in older adults.
Some controlled studies have shown that giving vitamin D to people who are deficient helps improve depression, including seasonal depression which occurs during the colder months. In the UK, this is often referred to as Seasonal Affective Disorder (SAD). The theory is that vitamin D effects the neurotransmitters in the brain, including serotonin, which regulates mood.
5. Impaired Wound Healing
Slow healing of wounds after surgery or injury may be a sign that your vitamin D levels are too low. Results from a test-tube study suggest that the vitamin increases the production of compounds that are crucial for forming new skin as part of the wound-healing process.
One study on people who had dental surgery found that healing was compromised in those with a deficiency. It has also been suggested that vitamin D’s role in controlling inflammation and fighting infection is important for proper healing. If your minor cuts take weeks rather than days to heal, this warrants investigation.
6. Bone Loss
Vitamin D plays a crucial role in calcium absorption and bone metabolism. Many older people who are diagnosed with bone loss believe they need to take more calcium. However, they may be deficient in vitamin D as well.
Low bone mineral density is an indication that your calcium and other minerals have been lost from bone. This places older adults, especially women, at an increased risk of fractures. In a large observational study of more than 1,100 middle-aged women in menopause or postmenopause, researchers found a strong link between low vitamin D levels and low bone mineral density.
7. Hair Loss
Hair loss is often attributed to stress, which is certainly a common cause. However, when hair loss is severe, it may be the result of a disease or a nutrient deficiency.
Hair loss in women has been linked to low vitamin D levels, though there is very little research on this to date. Alopecia areata is an autoimmune disease characterized by severe hair loss from the head and other parts of the body. It serves as a risk factor for rickets, which is a disease that causes soft bones in children due to vitamin D deficiency.
Low vitamin D levels are linked to alopecia areata and may be a risk factor for developing the disease. One study showed that topical application of a synthetic form of the vitamin successfully treated hair loss in a young boy with a defect in the vitamin D receptor.
8. Muscle Pain
The causes of muscle pain are often difficult to pinpoint. There is some evidence that vitamin D deficiency may be a potential cause of muscle pain in children and adults.
In one study, 71% of people with chronic pain were found to be deficient. The vitamin D receptor is present in nerve cells called nociceptors, which sense pain. A study in rats showed that a deficiency led to pain and sensitivity due to stimulation of nociceptors in muscles.
A few studies have found that taking high-dose vitamin D supplements may reduce various types of pain in people who are deficient.
9. Weight Gain
Obesity is a risk factor for vitamin D deficiency. A study in adults found a possible link between low vitamin D status and both belly fat and increased weight, although these studies are observational. This means it is unclear if the weight gain causes the low levels, or if the low levels contribute to weight gain.
However, the relationship is significant. Vitamin D is fat-soluble, meaning it gets stored in fat tissues. If you carry excess weight, your body may require higher amounts of vitamin D to maintain healthy blood levels compared to someone of a lower weight.
10. Anxiety
Vitamin D deficiency is linked to anxiety disorders. One study found that levels of calcidiol, a form of vitamin D, were lower in people with anxiety as well as in those with depression.
A separate study in pregnant women found that having sufficient vitamin D levels may help reduce anxious symptoms, improve sleep quality, and even help prevent postpartum depression. While more research is needed to confirm the mechanism, maintaining adequate levels is beneficial for overall mental health.
Common Risk Factors
While anyone can develop a deficiency, certain groups are at higher risk. Understanding these factors can help you determine if you should request a blood test from your GP.
- Skin Colour: The pigment melanin reduces the skin’s ability to make vitamin D in response to sunlight. Some studies show that older adults with darker skin are at high risk of deficiency.
- Environment: People who live in northern latitudes (such as the UK, Canada, and Northern Europe) or areas of high pollution, work night shifts, or are homebound are at high risk.
- Age: As you age, your kidneys are less able to convert vitamin D to its active form.
- Digestive Problems: People with Crohn’s disease, celiac disease, or cystic fibrosis may not absorb the vitamin effectively.
Treatment and Management
Correcting a vitamin D deficiency is generally simple, but it requires consistency. The most accurate way to measure how much vitamin D is in your body is the 25-hydroxy vitamin D blood test.
Dietary Sources vs. Supplements
While sun exposure is the primary source, dietary intake is supplementary. However, in the UK, the government advises that everyone should consider taking a daily vitamin D supplement during the autumn and winter.
| Source | Examples | Efficacy |
|---|---|---|
| Sunlight | Midday sun (10-30 mins) | High (dependent on season/skin) |
| Food | Salmon, Sardines, Egg Yolks | Low to Moderate |
| Fortified Food | Spreads, Cereals, Plant milks | Moderate |
| Supplements | D3 (Cholecalciferol) | High (Reliable) |
Most health organisations recommend a daily intake of 400–800 IU (10–20 micrograms), but people with a severe deficiency may need significantly higher doses prescribed by a doctor.
Practical Tips for Boosting Levels
- Get Outside: Aim for 10–30 minutes of midday sunlight several times a week. People with darker skin may need a little more than this.
- Eat Fatty Fish: Incorporate salmon, mackerel, or herring into your diet twice a week.
- Check Labels: Look for fortified foods. In the UK, many breakfast cereals and fat spreads are fortified by law or voluntarily.
- Consider Supplementation: Vitamin D3 is generally more effective than D2 at raising blood levels.
The Bottom Line
Vitamin D deficiency is incredibly common, yet the symptoms are often subtle and non-specific. From immune health to bone density and mental well-being, this nutrient is foundational to a healthy life.
If you think you may have a deficiency, it is important that you speak to your doctor or healthcare provider and get your blood levels measured. Correcting a deficiency is simple, easy, and can have profound benefits for your health.
Do not ignore the signs; maintaining adequate vitamin D levels is one of the easiest changes you can make to protect your long-term health.
Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with a healthcare professional for diagnosis and treatment.
